Summary Nonhuman primates (NHPs) have historically served as crucial animal models for diseases, and for testing of new therapies and vaccines that cannot be evaluated in rodents. Neotropical primates are used in biomedical research less frequently in the U.S. than Old World primates, but there is growing interest in these animals as models due to the close recapitulation of certain clinical diseases and simpler husbandry considerations. Studies involving marmosets and squirrel monkeys comprise the bulk of NIH-funded research featuring neotropical primates in several areas, including neurodegenerative disorders, infectious diseases, and aging. In this resource application, we propose to develop a number of marmoset and squirrel monkey antibodies to address the gap between project goals and available reagents. Species-matched antibodies can deplete targeted lymphocyte subsets and allow investigators to probe the impact of specific immune populations on progression, protection, and recovery. Diagnostic antibodies that distinguish antibody classes and subclasses, cell surface biomarkers, and soluble mediators will reduce limitations imposed by poor reagent accessibility. To derive these reagents, the squirrel monkey and marmoset immunoglobulin and Fcg receptor repertoire will be exhaustively defined and characterized. The antibody resources described here can raise the bar on neotropical primate translational research by providing investigators validated tools to evaluate the immune response in models of infectious or inflammatory disease.